Why two perfect display LUTs still don't match

Sensor, gamut, and white balance: three reasons two correct conversions still disagree.

The setup is familiar. A two-camera shoot. Sony FX6 in S-Log3, Canon C70 in C-Log3. Both display conversions picked from each maker's own pack. Drop the clips on the timeline.

They do not match. Not even close.

The answer is not "the conversions are wrong." They are doing exactly what they were built to do. The mismatch lives in three places upstream.

Reason 1. The sensor

Every sensor sees light a little differently. A Sony sensor and a Canon sensor record the same grass as two slightly different greens. Each maker's processing adds its own flavor on top.

A display conversion works on the encoded signal. It assumes the signal arrived encoded correctly. It cannot reach back and rebalance what the sensor actually saw.

So the FX6 conversion is correct for an FX6, the C70 conversion is correct for a C70, and the two correct conversions still give you two different pictures of the same scene. Because they started from two different captures of it.

Reason 2. The gamut

LOG is a tone curve plus a color space. S-Log3 lives in S-Gamut3.cine. C-Log3 lives in Canon Cinema Gamut. V-Log lives in V-Gamut. Each space is shaped a little differently.

The conversion does two jobs at once: roll the tone curve down to display range, and map the source gamut into Rec.709. Two different source gamuts give two different results, even from LOG that looks identical.

The fix is not to use the same conversion on both cameras. That breaks the tone curve. The fix is to accept that both conversions are right, then match the results to each other.

Reason 3. The white balance on set

The easiest one to forget, and often the biggest.

An A-cam locked to 5600K and a B-cam locked to 5200K record two different versions of the same light. A B-cam left on auto drifts shot to shot. A clip exposed half a stop hot comes out brighter and a touch more saturated.

White balance and exposure are single-axis fixes. The sensor and gamut differences are not; they are three-dimensional moves through the color volume. That is why they take hours by hand.

What this means in practice

A display conversion puts the picture into viewable range. It does not put two cameras in agreement. Two different jobs, and editors who try to do the second with the first spend an afternoon on curves.

Where MOVON fits

MOVON is the camera-match step. It reads the color of the reference and of each selected clip, then computes one grade per clip that pulls it toward the reference. It reads each clip as the camera recorded it, so there is nothing to prepare first.

Where this lands in the chain is at Where MOVON sits in your grading chain.